(300 ug will probably kill you. 50 might be more realistic)
I'd dooubt this would kill anyone IV. I read someone had eaten a 100ug/hr patch (7.2mg) and was fine. To me an entire 25ug/hour (1.8mg) is a good dose for a really powerfull experience, but I have do have some tolerance.
Maybe IV administration makes a big diffence. I still have some trouble believing its absolutely pure fentanyl, or just pure cut fentany. Its possibly pure, yet I think a chemist would have the decency to cut immadiately after making it, to prevent any mishaps.